The object of this invention is a process for preparing homo-and copolymers of vinyl chloride, in teh form of latexes, by polymerizing the corresponding monomer(s) in emulsion or in microsuspension. Another object is the resulting latexes as well as the homo- and copolymers derived from the said latexes.
Polymerization in "emulsion" is understood to mean polymerization, in the presence of a water-soluble initiator or initiators, of at least one monomer added to an aqueous medium containing at least one emulsifier.
Polymerization in "microsuspension" is understood to mean polymerization, in the presence of an organosoluble initiator or initiators, of at least one monomer dispersed by energetic mechanical means in an aqueous medium containing at least one emulsifier. "Energetic mechanical means" is used to mean a wide variety of conventional dispersion devices, among which might be mentioned, for example, colloid mills, high-speed pumps, vibratory agitators, and ultrasonic devices.
Polymerization in emulsion or in microsuspension is usually performed by bringing the reaction medium, under autogenous pressure and with moderate agitation, to a temperature generally between 10.degree. and 85.degree. C. and preferably between 30.degree. and 70.degree. C. and maintaining it there. After the pressure has dropped, the reaction is halted, and the unconverted momoner(s) is (are) eliminated by degassing the resulting polymer.
Processes for preparing homo- and copolymers of vinyl chloride by polymerizing the corresponding monomer(s) in emulsion or in microsuspension are carried out in reactors which are generally fitted with a double fluid circulation jacket and equipped with a paddle agitator with a rotating shaft and at least one deflector. The peripheral rotation speed of the agitator and the radial distance between the edge of the paddles and the deflector are such that the speed gradient between the paddles and the deflector is between 5 and 50 s.sup.-1. Such reactors are also equipped with a condensation cooling unit whose role is to extract from the reaction medium a portion of the heat deriving from the polymerization reaction, with the other portion being extracted by means of the circulation fluid in the double jacket. The said condensation cooling unit is generally of the reflux type, meaning that the liquefied phase produced by continuous condensation of the vapors emerging from the reaction medium continuously flows back into the said reaction medium.
According to the processes for preparing homo- and copolymers of vinyl chloride by polymerizing the corresponding monomer(s) in emulsion or in microsuspension utilized up to now, the peripheral rotation speed of the agitator is kept at a constant value of between 1 and 2 meters/second for the entire duration of the polymerization operation and the polymer degassing operation. These processes lead to the formation of a certain amount of crusts. If the processes occur at a peripheral agitator rotation speed of less than one meter/second, a smaller quantity of crusts is obtained, but the polymerization time becomes too long, and the conversion rate for the monomer(s) utilized becomes too low.